Oil circuit breakers (OCB""s) have been used since the early days of electrical power generation and distribution. For years, the OCB was the only practical type of circuit breaker for voltages between 15 and 230 kilovolts. Only since the 1980""s have other types of circuit breakers been able to slowly replace the OCB. The OCB still represents about 85 percent of all circuit breaker types in-service at these voltages.
The OCB""s purpose is to open under high current or overload conditions and thus protect the electrical lines, power distribution equipment, and attached electrical loads downstream. The occurrence of an OCB opening during heavy load conditions is usually referred to as a xe2x80x9cfault trip.xe2x80x9d One disadvantage of the OCB is that, after a relatively few number of fault trips, internal contacts become worn out and the oil inside becomes contaminated. This makes it necessary to remove the oil, filter or replace the oil, and replace any worn parts. Such maintenance is typically done many times over the expected life span of the OCB. A typical utility may have hundreds, perhaps thousands, of OCB""s to maintain.
While OCB""s typically have a target which is set to indicate that a fault trip has occurred, such targets do not store information showing how many fault trips have occurred since the last time the target was reset. Further, such targets do not provide any cumulative information concerning any fault trips which have occurred during a predetermined interval of time. And while computers have been used to measure current flows relating to trips and to estimate wear within a circuit breaker, such prior art equipment is far more complicated and expensive than necessary. What is needed is a simple way to predict when maintenance is needed so that labor and maintenance resources can be maximized.
Among the objects of the present invention are to provide improved fault trip indicators and maintenance methods which count and display the occurrences of a circuit breaker fault trip; to provide improved fault trip indicators which are reliable, durable, portable and compact; to provide improved fault trip indicators which are capable of ignoring a trip signal that does not coincide with a high current or overload condition; to provide improved fault trip indicators which display the fault trip count locally and/or provide a count signal over a communication line to a remote location; to provide improved fault trip indicators which use passive circuitry; to provide improved fault trip indicators which are easy to install; to provide improved fault trip indicators which are inexpensive to manufacture; and to provide improved maintenance methods for performing predictive maintenance on a circuit breaker.
Generally, one aspect of the invention is a fault trip indicator used with a circuit breaker. The circuit breaker is connected to protect an electrical line and has a protective circuit for opening the circuit breaker during a heavy load condition on the electrical line. The protective circuit includes a main current transformer which senses a current level flowing through the electrical line. The fault trip indicator has an auxiliary current transformer coupled to the main current transformer to produce a current signal which varies as a function of a current level produced by the main current transformer. A threshold detector is coupled to the auxiliary current transformer to produce a load signal when the threshold detector detects that the current signal exceeds a threshold value. The fault trip indicator also has a monitoring circuit coupled to the protective circuit and the threshold detector to provide an indication of the occurrence of the protective circuit opening the circuit breaker while the threshold detector is producing the load signal.
Another aspect of the invention is a fault trip indicator used with a circuit breaker. The circuit breaker is connected to protect an electrical line and has a protective circuit for opening the circuit breaker during a heavy load condition on the electrical line. The fault trip indicator includes a current transformer coupled to the electrical line to produce a current signal which varies as a function of a current level flowing through the electrical line. A battery-powered threshold detector is coupled to the current transformer to produce a load signal when the threshold detector detects that the current signal exceeds a threshold value. The fault trip indicator also has a monitoring circuit coupled to the protective circuit and the threshold detector to provide an indication of the occurrence of the protective circuit opening the circuit breaker while the threshold detector is producing the load signal.
Yet another aspect of the invention is a fault trip indicator used with a circuit breaker. The fault trip indicator is connected to protect an electrical line and has a protective circuit for opening the circuit breaker during a heavy load condition on the electrical line. The fault trip indicator includes a current transformer coupled to the electrical line to produce a current signal which varies as a function of a current level flowing through the electrical line. A threshold detector is coupled to the current transformer to produce a binary load signal when the threshold detector detects that the current signal exceeds a threshold value. The fault trip indicator also has a monitoring circuit coupled to the protective circuit and the threshold detector to provide an indication of the occurrence of the protective circuit opening the circuit breaker while the threshold detector is producing the binary load signal.
Still another aspect of the invention is a fault trip indicator used with a circuit breaker. The circuit breaker is connected to protect an electrical line and has a protective circuit for opening the circuit breaker during a heavy load condition on the electrical line. The fault trip indicator includes a current transformer coupled to the electrical line to produce a current signal which varies as a function of a current level flowing through the electrical line. A passive threshold detector is coupled to the current transformer to produce a load signal when the threshold detector detects that the current signal exceeds a threshold value. The fault trip indicator also has an indicator coupled to the protective circuit and the threshold detector to provide an indication of the occurrence of the protective circuit opening the circuit breaker while the threshold detector is producing the load signal.
Yet still another aspect of the invention is a method of performing maintenance on a circuit breaker where the circuit breaker is connected to protect an electrical line and has a protective circuit for opening the circuit breaker during a heavy load condition on the electrical line. The method includes producing a current signal which varies as a function of the current level flowing through the electrical line and establishing a first threshold value. The method also includes producing a binary load signal as a function of the current signal and the first threshold value. The method further includes providing an indication of the occurrence of the protective circuit opening the circuit breaking while the binary load signal is being produced. The method further includes establishing a second threshold value and performing maintenance on the circuit breaker as a function of the indication and the second threshold value.
Yet still another aspect of the invention is a method of performing maintenance on a circuit breaker where the circuit breaker is connected to protect an electrical line and has a protective circuit for opening the circuit breaker during a heavy load condition on the electrical line. The method includes producing a current signal which varies as a function of the current level flowing through the electrical line and establishing a first threshold value. The method also includes using battery power to produce a load signal as a function of the current signal and the first threshold value. The method further includes providing an indication of the occurrence of the protective circuit opening the circuit breaking while the load signal is being produced. The method further includes establishing a second threshold value and performing maintenance on the circuit breaker as a function of the indication and the second threshold value.
Other objects and features will be in part apparent and in part pointed out hereinafter.